The present invention relates to a power transmission system for a tractor for example of the fourwheel drive type in which a hydraulic pump and a hydraulic motor are used.
Power transmission systems for tractors must be operable to transmit the power from an engine to a wheel drive mechanism and to a power takeoff (PTO) transmission mechanism for operating various working implements. It is essentially required for tractor works that the wheel transmission mechanism and the PTO transmission mechanism be independent of each other for the power transmission.
Accordingly conventional systems include a separate transmission path for transmitting the power from the engine to the PTO transmission mechanism before the power is delivered to the wheel transmission mechanism through a hydraulic motor. Thus the input shaft for the PTO transmission mechanism is provided under or on one side of the hydraulic pump and motor and the wheel transmission mechanism to bypass them, such that a transmission shaft for giving the engine power to the hydraulic pump delivers the power to the input shaft positioned therebelow by way of gears.
This arrangement has the drawback of being very bulky since the hydraulic motor and the bypass PTO input shaft are positioned below the hydraulic pump. The arrangement also involves the necessity of delivering the power from the hydraulic pump input shaft to the PTO input via gears.
This invention has overcome these drawbacks of the prior art.